A typical color camera separately monitors red, green, and blue components of an image. Electronic imagers rely on some means of separation of the illumination incident on the sensor into a number of spectral channels. Widely-used means of discrimination between spectral components of the imaging scene include the Color Filter Arrays (usually employed in systems based on single focal plane array) and beam-splitting prisms (primarily employed in systems based on multiple focal plane arrays). In either case, the incident illumination is separated into a small number, usually 3 or 4, discrete color (spectral) channels.
For any given scene, the exact ratio of color channel values will depend on the spectral characteristics of the entire optical stage of the imager. This is typically done using a color filter array over a photosensitive area. The color filter array is formed of a plurality of different colored elements, which respectively pass only color of a predetermined spectral parameter.
A typical color filter array is shown in FIG. 1A. Each of the boxes such as 100 represents a single pixel. Each set of four boxes outlined by the line 102 can be considered as a megapixel. The pattern in the megapixel repeats throughout the entire color filter array grid.
Spectral channels of the modern color imagers do not have the same spectral sensitivities as color-sensitive elements, the cones, of the human eye. FIGS. 1B-1D respectively illustrate the spectral sensitivity curves of the human eye (β, γ, ρ) and spectral transmittances of the red, green and blue color channels typical for modern RGB electronic imaging systems. As a consequence, the direct use of individual color channels values of the imager as stimuli for typical display devices, such as VGA or NTSC monitors, does not lead to correct color rendition. Hence, colors are corrected color signals detected by the electronic imaging system into color channel stimuli appropriate for the output to the image rendering device.
Each megapixel 102 has two green filters, one red filter, and one blue filter. This is because the eye is usually more sensitive to green than it is to red and blue.
The intent of the filter of FIG. 1A is to provide an image which is precisely matched to the spectral content of the eye. However, this filter, while it does the best that it can, is not precisely matched. It is often desirable to interpolate between the values.
For example, the value received at area 100 is only indicative of the green portion impinging on area 100. However, some part of that incoming light is also red. Another part of the incoming light is also blue. Hence, each of the pixels is processed according to a transformation to solve the equation:R=K11R+K12G+K13B G=K21R+K22G+K23B B=K31R+K32G+K33B 
This transformation completely defines the system. This includes the so-called color transformation matrix:                K11 K12 K13         K21 K22 K23         K31 K32 K33         